Welding head for friction stir welding

ABSTRACT

The friction stir welding head presented herein includes a head housing and an axle. The head housing extends from a top end to an open bottom end and defines a bore extending between the top end and the open bottom end. The axle that is coaxial with and rotatable within the bore. The axle is also laterally secured within the head housing and axially movable with respect to the head housing. Still further, the axle includes an engagement end that extends beyond the open bottom end of the head housing. The engagement end supports a friction stir welding tool that is configured to rotate with the axle to effectuate friction stir welding operations. The friction stir welding head may also include a load cell configured to generate load signals in response to axial movement of the axle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/941,092, filed Mar. 30, 2018, and entitled “Welding Head for FrictionStir Welding,” the entire contents of which are incorporated byreference herein.

TECHNICAL FIELD

The present disclosure is directed towards a welding head for frictionstir welding (FSW) and, in particular, a compact FSW head with improvedaxial force measurement.

BACKGROUND

Friction stir welding (FSW) is a welding process which uses heatgenerated from high-pressure friction to form a joint between twoworkpieces and/or to fix cracks in a workpiece. That is, during FSWoperations, an FSW tool traverses a joint or seam disposed between theworkpieces (or a crack in a workpiece) and the workpiece(s) areplasticized by frictional heat generated by rotation of the FSW tool. Asthe FSW tool traverses the seam, the FSW tool is also pressed againstthe workpieces, which are fixed relative to each other during thewelding operation. More specifically, an FSW tool includes a shoulderand a pin or probe that extends out from the shoulder. During thewelding operation, the shoulder is pressed against the workpiece(s) andthe pin rotates in the seam between the workpieces (or in a crack in aworkpiece). In some FSW heads, the shoulder rotates with or relative tothe pin, but in other FSW heads, the shoulder may be stationary.Rotation of the pin (and the shoulder in some instances), softens andmixes the materials forming the workpieces. Then, the mixed materialsconsolidate to form a solid-state weld.

The FSW tool can traverse a seam (or crack) when the welding tool movesrelative to the workpiece(s) and/or when the workpiece(s) are movedrelative to the welding tool (e.g., the welding tool may be stationary).Regardless, during FSW, the welding tool must be pressed against theworkpieces with great force to frictionally heat the workpieces enoughto cause the desired plasticizing in the seam, and it is important toknow the axial force acting on the tool and workpieces to properlycalibrate and control the FSW operations (and perhaps, to adjust abacking) to provide high-quality welds. Thus, typically, FSW headsinclude a force measuring sensor, such as a load cell, and it isimportant that the force measuring sensor provides accurate data.

SUMMARY

The present disclosure is directed towards a friction stir welding (FSW)head. According to one embodiment, the FSW head includes a head housingand an axle. The head housing extends from a top end to an open bottomend and defines a bore extending between the top end and the open bottomend. The axle is coaxial with and rotatable within the bore. The axle isalso laterally secured within the head housing and axially movable withrespect to the head housing. Still further, the axle includes anengagement end that extends beyond the open bottom end of the headhousing. The engagement end supports an FSW tool that is configured torotate with the axle to effectuate FSW operations. Advantageously, theaxial movement of the axle allows the axle to impart axial forces to aload cell disposed within or beneath the head housing. Additionally, theaxial movement of the axle may allow the welding head to transitionbetween rotating shoulder FSW and stationary shoulder FSW with a singleoperation.

In at least some of these embodiments, the FSW head also includes amotor assembly configured to rotate the axle within the bore and withrespect to the head housing. Consequently, the FSW welding head may notneed to be installed on a spindle or spindle actuator. Instead, the FSWhead can be mounted on a robot, gantry, or any other carrier that movesthe FSW head into place and supplies power to the motor assembly and theFSW head will supply its own rotational forces.

As mentioned, the FSW head may, in addition or as an alternative to themotor assembly, include a load cell configured to generate load signalsin response to axial movement of the axle. In some of these embodiments,the load cell is disposed beneath the open bottom end of the headhousing. Alternatively, the load cell may be disposed between the openbottom end of the head housing and the top end of the head housing.Advantageously, positioning the load cell in either of these positionsthe load cell close to the FSW tool which may increase the accuracy ofthe load signals. For example, if the load cell is positioned beneaththe open bottom end of the head housing, axial forces exerted on the FSWtool may act nearly directly on the load cell.

As more specific examples, in some embodiments including a load cell,the load cell includes an inner ring and outer ring. The inner ring isfixedly coupled to the axle and movably coupled to the outer ring via aflexible portion, and relative movement of the inner ring with respectto the outer ring causes the load cell to generate the load signals. Insome of these embodiments, the tool includes a pin and a shoulder thatrotates with the pin to effectuate the FSW operations. Then, when upwardforces act on the shoulder, the upward forces are translated to theinner ring to move the inner ring with respect to the outer ring andcause the load cell to generate the load signals. Specifically, in someembodiments, a lower bearing enables the axle to rotate with respect tothe head housing and the lower bearing is either coupled to the innerring via one or more floating components or formed with the inner ringand the one or more floating components, so that the upward forces onthe shoulder translate to the inner ring via the lower bearing and theone or more floating components. Alternatively, in other embodiments,the tool includes a pin and a shoulder that is covered by a stationaryshoulder. In these embodiments, upward forces on the stationary shoulderare translated to the inner ring to move the inner ring with respect tothe outer ring and cause the load cell to generate the load signals. Forexample, the upward forces may translate directly from the stationaryshoulder to the inner ring.

According to another embodiment, an FSW head includes a head housing,one or more floating components, and a load cell. The head housingextends from a top end to an open bottom end and defines a boreextending between the top end and the open bottom end. The one or morefloating components are configured to support an FSW tool and the one ormore floating components are axially movable with respect to the headhousing. The load cell is disposed beneath the open bottom end of thehead housing and configured to generate load signals in response toaxial movement of the floating components. As mentioned, when the loadcell is positioned beneath the head housing, the load cell is positionedclose to the FSW tool which may increase the accuracy of load signalsgenerated by the load cell. For example, if the load cell is positionedbeneath the open bottom end of the head housing, axial forces exerted onthe FSW tool may act nearly directly on the load cell. Moreover, whenthe load cell is positioned beneath the head housing and the FSW headincludes one or more floating components, it may be relatively simple toswitch between rotating shoulder FSW operations and stationary shoulderFSW operations.

In some of these embodiments, the one or more floating componentsinclude an axle that is coaxial with the bore, one or more bearings thatallow rotation of the axle within the bore, and a connector ring thatconnects a particular bearing of the one or more bearings to the loadcell. Additionally, the one or more floating components may include aninner ring of the load cell. The inner ring is fixedly coupled to theaxle via at least the connector ring and is also movably coupled to anouter ring of the load cell via a flexible portion so that relativemovement of the inner ring with respect to the outer ring causes theload cell to generate the load signals. Additionally or alternatively,the one or more floating components may include a rotor of a motorassembly. The rotor is movable by a stator that is fixedly coupled tothe head housing to effectuate rotation of the axle within the bore. Asmentioned, if the head includes a motor assembly (e.g., if the one ormore floating components include a rotor of a motor assembly), the FSWwelding head need not be installed on a spindle or spindle actuator.Instead, the FSW head can be mounted on a robot or gantry that moves theFSW head into place and supplies power to the motor assembly. The othercomponents mentioned above may axially and longitudinally secure theaxle within the head housing and ensure that axial forces acting on theaxle are translated to the load cell.

In embodiments where the one or more floating components include one ormore bearings that allow rotation of the axle within the bore, onebearing may be a lower bearing disposed between the load cell and amotor assembly included in the FSW head. In some of these embodiments, asupplemental bearing housing is disposed coaxially outward from thelower bearing and is accessible via an access panel included on the headhousing. This may allow the lower bearing to be easily serviced and/orreplaced, without disassembling other components of the FSW head.

Still further, in some embodiments, the FSW head is reconfigurablebetween a rotating shoulder configuration and a stationary shoulderconfiguration with a single installation operation. For example, astationary shoulder housing may be simply coupled or decoupled to thehead. This is advantageous because it allows for nearly seamlesstransition between these two types of FSW operations. By comparison,other FSW heads may need to be completely removed/replaced to effectuatesuch a change, which will not only be less efficient in terms of time,but also in terms of cost (the cost of acquiring and maintaining two FSWheads is likely to be much higher than the cost of acquiring one headand reconfiguring the head with a single operation).

According to yet another embodiment, a method of FSW is presentedherein. The method includes providing a head housing that extends from atop end to an open bottom end and defines a bore extending between thetop end and the open bottom end and installing a floating axle in thehead housing. The floating axle includes an engagement end that extendsbeyond the open bottom end and supports an FSW tool. The method alsoincludes installing a load cell on the open bottom end of the headhousing and controlling FSW with the tool based on load signalsgenerated by the load cell.

In some of these embodiments, the FSW is rotating shoulder FSW and themethod further includes transitioning to stationary shoulder FSW byinstalling a stationary shoulder housing onto the load cell. In some ofthese embodiments, the stationary shoulder housing covers a shoulder ofthe FSW tool and the transitioning is complete with a single operation.That is, the no other components of the welding head, aside from thestationary shoulder housing, may need to be altered, removed, installed,etc. to effectuate the transition. As mentioned above, using a single,reconfigurable head may be more efficient in terms of time and cost ascompared to using two heads for these two operations. This is especiallytrue when the transitioning comprises a single operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of a friction stir welding (FSW) head,according to a first example embodiment of the present disclosure.

FIG. 2 is a partially exploded, sectional perspective view of the FSWhead of FIG. 1, with the FSW head being shown in a sideways orientation.

FIG. 3 is a sectional perspective view of the FSW head of FIG. 1.

FIG. 4 is another sectional perspective view of the FSW head of FIG. 1that illustrates a force path from a FSW tool included in the FSW headto a load cell included in the FSW head.

FIG. 5 is a side perspective view of the FSW head of FIG. 1 whilereconfigured in accordance with a stationary shoulder configuration.

FIG. 6 is a partially exploded, sectional perspective view of the FSWhead of FIG. 1 while in the stationary shoulder configuration shown inFIG. 5.

FIG. 7 is another sectional perspective view of the FSW head of FIG. 1that illustrates a force path from the FSW tool to the load cell whenthe FSW head of FIG. 1 is in the stationary shoulder configuration shownin FIG. 5.

FIG. 8 is a sectional perspective view of an FSW head, according to asecond example embodiment of the present disclosure, with the FSW headbeing shown in a sideways orientation.

Like numerals identify like components throughout the figures.

DETAILED DESCRIPTION

A compact friction stir welding (FSW) head with improved axial forcemeasurement (e.g., along an axial or vertical direction of the head) isprovided herein. The FSW head provides improved downward forcemeasurement because the FSW head includes a “floating” axle and a loadcell that is disposed on a bottom of the head, adjacent an engagementend (e.g., a welding end) of the floating axle. The axle is “floating”because the axle can travel, at least slightly, in an axial direction(e.g., longitudinally or vertically) with respect to a main body orhousing (also referred to herein as the head housing) of the FSW head.The position of the load cell and the range of longitudinal movement ofthe axle allow the load cell to accurately measure axial forces.Moreover, positioning the load cell at the bottom head and providing afloating axle creates a compact FSW head that is stiff, sturdy, and easyto service. These concepts can be utilized to create compact FSW headsof all sizes, with a rotating or stationary shoulder. In fact, in atleast some embodiments, the FSW head presented herein can easilytransition (e.g., with a single operation) between a rotating shoulderconfiguration and a stationary shoulder configuration.

FIGS. 1-7 illustrate an FSW head 10 according to a first exampleembodiment. In FIGS. 1-4, the head 10 is shown in a rotating shoulderconfiguration C1. In FIGS. 5-7 the head 10 is shown in a stationaryshoulder configuration C2. As is explained in further detail, the head10 can transition between these configurations with a single operation,without disassembling the head 10. However, before turning to thisaspect of the head 10, the head 10 is described in connection with FIGS.1-4.

First turning to FIG. 1, the head 10 includes a head housing 100 and anaxle 202. The head housing 100 extends from a first or top end 102 to asecond or bottom end 104. The top end 102 can be attached to a robot,gantry, or other such holding structure. Meanwhile, the bottom end 104is open so that the housing 100 defines a closed-end bore 106 that isopen at the second end 104, but closed at the first end 102, as is shownin FIG. 2. That is, the bottom 104 is an open, bottom end 104. The axle202 is coaxial with a central axis of the housing 100 and extendsthrough the bore 106 of the housing 100 in an axial or longitudinaldirection so that the axle 202 extends beneath the bottom end 104 of thehousing 100. An FSW tool 280 that defines a shoulder and pin/probeduring FSW is coupled to a bottom end 204 of the axle 202 (the bottomend 204 may also be referred to as the welding or engagement end 204).

In the embodiment depicted in FIG. 1, an annular load cell 250 is alsopositioned beneath the bottom end 104, so that the load cell 250 isadjacent or proximate the engagement end 204 of the axle (and the tool280). Generally, the load cell 250 generates load signals as a functionof forces exerted on the engagement end 204 of the axle 202 (by way ofthe tool 280). In other words, and as is explained in further detail inconnection with FIGS. 4 and 8, as the tool 280 acts against a workpiece,the axle 202 will move slightly upwards (e.g., translate verticallyabout 0.1 mm, or more generally in the range of 0.01-1.0 mm) withrespect to the housing 100, pushing or pulling a portion of the loadcell 250 so that the load cell 250 generates load signals as a functionof the longitudinal forces exerted on the bottom end 204 of the axle 202(by way of the tool 280). By comparison, many other FSW solutionsinclude load cells above the welding head 10 (e.g., at or adjacent topend 102), which may create inaccuracies in the load signals generated bythe load cell 250 (due to the distance between the point where the forceis exerted and the point where the signals are generated).

Any signals generated by the load cell may be transmitted to acontroller 40, which converts the load signals into force measurements(e.g., digital data) that can be used to control the FSW operations andensure a high-quality weld. That is, the controller may accumulate datafrom the load signals and determine whether the downward force appliedto the FSW head needs to be altered, for example, to ensure completepenetration with the FSW tool 280. Force measurements can be takencontinuously and are used to maintain the force at a desired levelthroughout the welding process to produce a smooth surface and desiredcharacteristics of the weld. Depending on the requirements of aparticular welding process or workpiece, the target force level can beprogrammed to vary during sections of a weld. Further, the forcemeasured throughout a welding process can be recorded (e.g., the forcecan be recorded on a time basis or as a function of the position of thewelding head relative to the workpiece). Optionally, controller 40 canbe configured to generate a visual or aural warning in the event theforce deviates from a target force level.

Still referring to FIG. 1, overall, the welding head 10 is compact anddoes not require external forces (e.g., from a spindle drive/actuator,etc.). That is, the welding head 10 has relatively small externaldimensions and may be a relatively self-contained FSW head, insofar asthe head may operate without an external drive mechanism (but may stillneed to be coupled to a power source, controller, and/or a holdingdevice, such as a gantry). As an example of the external dimensions ofthe welding head 10, the welding head 100 may have an external diameterin the range of approximately 100 mm to approximately 500 mm and anexternal longitudinal dimension (e.g., a height) in the range ofapproximately 200 mm to approximately 1,000 mm. As one specific example,for a typical welding thickness up to 12 mm, the welding head 100 mayhave an external diameter of approximately 355 mm and an externallongitudinal dimension (e.g., a height) of approximately 250 mm. Thiscompact design reduces deviation (bend) created on a holding structure(robot, gantry, etc.) and also minimizes the chances of the head 10colliding with portions of the workpiece, portions of a holdingstructure, or other such objects during FSW operations.

FIGS. 2 and 3 show a more detailed description of the componentsincluded in head 10. In FIG. 2, the head 10 is shown with componentsremoved from the housing 100 to illustrate the portions of the head 10that are “floating” with respect to the housing. For clarity, in FIG. 2,the floating components 200, which include the axle 202, upper bearing210, lower bearing 212 (and the lower bearing housing 214), a spacer216, a connecting ring 220, an inner ring 252 of the load cell 250, anda rotor 154 of the motor assembly 150 are shown within a dashed line.Notably, although the inner ring 252 of the load cell 250, as well as arotor 154 (which is part of motor 150), are coupled to and move with thefloating components 200 (and, thus, may be considered floatingcomponents) the entirety of the load cell 250 and the entirety of themotor assembly 150 are not floating with the axle 202. Instead, themotor 150 and load cell 250 each include portions that are fixed to thehead housing 100 (a stator 152 and an outer ring 256, respectively).FIG. 3 shows the same sectional view as FIG. 2 (albeit rotated 90degrees), but with the head 10 fully assembled.

In the embodiment depicted in FIGS. 2 and 3, the head housing 100includes a rotational motor 150 with a stator 152 that is fixedlycoupled to the head housing 100 and a rotor 154 that is fixedly coupledto a central portion of the axle 202, between the upper bearing 210 andthe lower bearing 212. The rotor 154 may be mechanically spaced from thelower bearing 212 and the load cell 250 by a radial spacer 216 to ensurethat the rotor 154 does not become magnetically stuck and/or damagedwhen the lower bearing 212 is serviced. Meanwhile, the stator 152 isfixed to the head housing 100 and can be liquid cooled via inlet/outlet156 and inlet/out 158 (one of items 156 and 158 will be an inlet and theother is an outlet, but flow may be reversible; thus, each is labeled asinlet/outlet). Generally, the motor 150 may impart rotational motion tothe axle 202 (and, thus, to the tool 280).

At a high level, the axle 202 is a rotatable body that extends from (orthrough) the top end 102 of the housing 100 to (or through/out of) thebottom end 104 of the housing 100. The axle 202 may be substantiallycylindrical; however, the axle may also include various steps,depressions, receptacles, and other such features that allow the axle tobe floatingly secured within the head housing 100, insofar as“floatingly secured” means that the axle 202 is laterally secured (sothat the axle cannot tilt or translate laterally), but movable axiallywithin the head housing 100. For example, in the embodiment depicted inFIGS. 1-7, the axle 202 includes various steps (e.g., sections ofdifferent diameters) that secure the axle laterally without preventingaxial movement of the axle 202. In the embodiment depicted in FIGS. 2and 3, the axle 202 is widest at a central segment 203 that isconfigured to engage the motor assembly 150. Moreover, to ensure thecentral segment 203 remains engaged with the motor assembly 150 (or morespecifically, that rotor 154 remains engaged with stator 152), thebottom end (leftmost end in FIG. 2) of the central segment 203 includesa peripheral flange that extends between the lower bearing 212 andradial spacer 216. Moving downwards (or right to left in FIG. 2) fromcentral segment 203, the axle 202 may include a number of diameterreducing steps that may serve to laterally lock various components intoplace between the axle 202 and head housing 100 and/or that simplyreduce the diameter of axle 202 towards the lower end 204 of the axle202, where tool 280 is secured to the axle 202.

To secure the tool 280, the lower end may include an axial cavity sizedto receive a body of the tool 280. The cavity may have any desirablesize and may also include a locking feature 286, such as a threadedscrew, that allows any desirable tool 280 to be secured to the axle 202.The tool 280 protrudes (e.g., extends downwards) from the lower end 204of axle 202 and defines a shoulder 284 and a pin or probe 282 that willcreate a joint in or between one or more workpieces. In the depictedembodiment, the shoulder 284 is substantially orthogonal to the axialdirection (the direction in which pin 282 extends) and the pin 282 has atruncated conical shape; however, in other embodiments, the operatingend of the tool 280 may have any desirable shape and/or include anydesirable features (e.g., the pin may include threads). Additionally, inother embodiments, the pin 282 may be movable with respect to theshoulder 284 (e.g., retractable) and/or include any other FSW featuresnow known or developed hereafter.

Additionally, in the depicted embodiment, the axle 202 includes aninternal bore or passage 206. The passage 206 is configured to alignwith cooling features included in the tool 280 and with coolant deliveryfeatures included in the head housing 100. For example, in the depictedembodiment, the top end 102 of the head housing 100 includes an inlet112 and an outlet 114 for gas or liquid coolant. Coolant delivered viainlet 112 enters the passageway 206 via conduit 120 so that the coolantcontacts the tool 206 and axle 202 adjacent the lower end 204 of theaxle 202. Then, the coolant travels upwards, around the conduit 120 andexits the passageway 206 via the outlet 114. However, in otherembodiments, the head 10 may include any desirable cooling features tocool the axle 202 and/or the tool 280.

Still referring to FIGS. 2 and 3, the upper bearing 210 (or at least ahousing including bearing 210) and the lower bearing 212 (or at least ahousing including bearing 210) are also coupled (e.g., an inner edge ofthe bearing is fixedly coupled to the axle 202) to the axle 202 so thatthe axle 202 (and the tool 280) can spin with respect to the housing 100as the motor 150 rotates the axle 202. The upper bearing 210 is disposedabove the motor 250 and the lower bearing 212 is disposed below themotor 150 to minimize friction immediately adjacent the motor 250. Ascan be seen in FIG. 3, in the depicted embodiment, the upper bearing 210is biased longitudinally upwards by biasing member 211. This biasing mayensure that the axle 202 remains axially fixed during servicing ofbearings, the load cell, and/or any other component (or when not inuse). In other embodiments, the head 10 need not including biasingmember 211; however, if the head 10 includes biasing member 211, theload cell 250 may calibrate for this biasing by zeroing out prior to anFSW operation.

The lower bearing 212 is supported by a supplemental bearing housing 214that is disposed coaxially outward from the bearing 210. Bearing housing214 extends substantially between the lower bearing 212 and the headhousing 100 so that the bearing housing is adjacent the housing 100(although some clearance may be provided between the head housing 100and the bearing housing 214 so that the housing 214 does not get stuckon the head housing 100 due to swelling from heat generated during FSWoperations). Due to this position, the bearing housing 214 may beaccessible via an access panel 215 (see FIG. 5) included in the housing100 so that bearing 212 can be serviced/replaced without disassemblingany other components of the head 10. The head housing 100 may alsoinclude an O-ring 108 configured to support and center the bearinghousing 214.

Still referring to FIGS. 2 and 3, but now with reference to FIG. 4 aswell, the connector ring 220 is coupled to and extends between the loadcell 250 and the bearing housing 214. More specifically, in at leastsome embodiments, the connector ring 220 is fixedly coupled to the innerring 252 of the load cell 250 and fixedly coupled to the bearing housing214. Alternatively, the connector ring 220, the inner ring 252 of theload cell 250, and the bearing housing 214 may be formed integrally(i.e., as one piece), which might decrease the overall height(longitudinal dimension) of the head 10. Regardless, the bearing housing214 is fixedly coupled to the axle 202 (via bearing 212) and, thus, theconnector ring 220 ensures that that inner ring 252 of the load cell 250moves or floats with the axle 204. On the other hand, the inner ring 252is also flexibly coupled, via a flexible portion 254, to the outer ring256 of the load cell, which is fixedly coupled to the head housing 100.Thus, any “floating” of the axle may cause the load cell 250 to generateload signals due to the relative movement of the inner ring 252 withrespect to the outer ring 256.

For example, in the example embodiment depicted in FIGS. 1-4, when thetool 280 is acting on one or more workpieces, the axle 202 will floatupwards and pull the inner ring 252 upwards with respect to the outerring 256, as is demonstrated by force path P1. As is shown in FIG. 4,force path P1 generates a force F1 in the load cell 250, thereby causingthe load cell 250 to generate load signals. The load signals may betransmitted upwards through the head 10 via a transmission member 258,so that a data connection can transfer the signals from the head 10 tothe controller 40 (see FIG. 1). In the depicted embodiment, the axle 202(and any other floating components 200 fixedly coupled to axle 202) maymove approximately 0.1 mm. This small amount of axial movement issufficient for the load cell 250 (e.g., a column load cell) to measureaxial (e.g., longitudinal) forces being applied to the tool 280.

Now turning to FIGS. 5-7, the FSW head 10 is shown when reconfiguredinto a stationary shoulder configuration C2. Notably, due to theplacement of the load cell 250 and the floating components 200, the head10 can easily be reconfigured from a rotating shoulder configuration C1(FIGS. 1-4) to a stationary shoulder configuration C2. To effectuate thechange, a stationary shoulder housing 300 is simply coupled to the innerring 252 of the load ring 250 with a single operation. No componentsneed to be removed from the head 10 during this single operation. Sincethis change in configurations is relatively straightforward, only thedifferences between FIGS. 5-7 and FIGS. 1-4 are discussed below and anydescription of like parts included above is to be understood to apply tothe components shown in FIG. 5-7 unless differences are described below.

Most notably, since the stationary shoulder housing 300 (e.g., a “bellhousing”) is installed over the lower end 204 of the axle 202, the axle202 is no longer visible from an exterior of the head 10 (as shown inFIG. 5). In fact, even the shoulder 284 of the tool 280 is obscured froman exterior of the head 10 and, instead, the stationary shoulder housing300 provides a stationary shoulder 302 for the pin 282, which protrudesfrom a small opening 304 included at a center of the bottom of thestationary shoulder housing 300.

Still referring to FIGS. 5-7, but now with an emphasis on FIGS. 6 and 7,when the stationary shoulder housing 300 is coupled to the head housing100, it is connected to the inner ring 252 of the load ring 250 via aconnector 320. Consequently, if upward pressure is applied to thestationary shoulder 300 (e.g., at shoulder 302), the stationary shoulder300 will push directly on the inner ring 252 of the load cell 250. Sincethe inner ring 252 is coupled to the floating axle 202, the inner ring252 can float (e.g., move vertically) upwards, at least slightly, withrespect to the outer ring 256 and cause the load cell 250 to generateload signals. More specifically, when the tool 280 is acting on one ormore workpieces, upward force will be applied to the load cell alongforce path P2, as is shown in FIG. 7. Force path P2 generates a force F2in the load cell 250 (like path P1 generating a force F1, except now theforce is generated via pushing directly on the load cell instead ofpulling indirectly on the load cell), thereby causing the load cell 250to generate load signals. Again, the load signals may be transmittedupwards through the head 10 via a transmission member 258, so that adata connection can transfer the signals from the head 10 to thecontroller 40 (see FIG. 5). As mentioned, in the depicted embodiment,the axle 202 (and any other floating components 200 fixedly coupled toaxle 202) may move approximately 0.1 mm and this small movement issufficient for the load cell 250 to measure axial (e.g., longitudinal)forces being applied to the tool 280.

Now turning to FIG. 8, which illustrates another embodiment of an FSWhead 20 with improved axial force measurement. Although the embodimentdepicted in FIG. 8 is a different embodiment as compared to theembodiment shown in FIGS. 1-7 (as opposed to a reconfiguration), theembodiment shown in FIG. 8 is still quite similar to the embodimentsshown in FIGS. 1-7. Consequently, the differences between FIG. 8 andFIGS. 1-7 are discussed below and any description of like parts includedabove is to be understood to apply to the components shown in FIG. 8unless differences are described below.

For example, in the embodiment illustrated in FIG. 8, the axle 202 has adifferent shape than embodiments shown in FIGS. 1-7, but, overall, theaxle 202 is still a floating axle; thus, any description of the floatingaxle 202 included above (aside from descriptions of the shape of theaxle in FIGS. 1-7) is applicable to the axle 202 shown in FIG. 8. InFIG. 8, the most notable difference from FIGS. 1-7 is that the load cell250 has been moved from the bottom end 104 of the head housing 100 to alocation between the motor assembly 150 and the lower bearing 212 (whichnow includes three rows of bearings, as opposed to two, but otherwiseoperates, and is accessible, in the same manner as bearing 212 fromFIGS. 1-7). This location may provide protection for the load cell 250and may still be sufficient to generate load signals during rotatingshoulder FSW operations. For example, during rotating shoulder FSW, therelative movement of the axle 202 and the lower bearings 212 withrespect to the head housing 100 (and the outer ring 256 of the load cell250) generates an upward axial force (left to right in FIG. 8) on theinner ring 252 of the load cell 250, which causes the load cell togenerate load signals. However, due to this location it may not bepossible to reconfigure head 20 for stationary shoulder FSW since theshoulder would not be able to apply a direct force to the load cell 250(e.g., stationary shoulder housing 300 could not be coupled to and acton the load cell 250).

The FSW head presented herein provides a number of advantages. Forexample, the FSW head presented herein provides a compact and largelyself-contained FSW head that can operate on various holding structures(e.g., a gantry, robot, etc.) while minimizing the chances of collidingwith workpieces, parts of a holding structure or any other objects. Thecompact size of the FSW head presented herein also ensures that the FSWhead is stiff and study while reducing the odds that the FSW head willcause a deviation (e.g., bend) in a holding structure (e.g., a gantry,robot, etc.). Moreover, the FSW provides improved measurement of axialforces (e.g., forces acting along the central axis of the welding head,such as upward or downward forces) because the path between the loadcell and the FSW tool is greatly reduced, especially as compared tosolutions that position a load cell above the FSW head. The pathreduction results in improved accuracy which, in turn, allows acontroller to provide improved (e.g., more accurate) operationalparameters (e.g., travel speed, downward force, etc.) that create higherquality welds.

Still further, in at least some embodiments, the FSW head providesimproved serviceability at least because the load cell and the lowerbearings are easily accessible. Thus, the load cell and/or the lowerbearings may be accessed and repaired/replaced without extensivedeconstruction of the welding head. For example, the load cell and/orthe lower bearings may be replaceable without removing the FSW head froma holding structure (e.g., a gantry, robot, etc.). Furthermore, in atleast some embodiments (e.g., the embodiment shown in FIG. 1-7), the FSWhead presented herein is advantageous because it may quickly and easilybe reconfigured between a configuration suitable for rotating shoulderFSW and a configuration suitable for stationary shoulder welding (i.e.,by simply installing or removing a stationary shoulder housing onto theFSW head).

To summarize, in one form, a FSW head is provided, the FSW headcomprising: a head housing that extends from a top end to an open bottomend and defines a bore extending between the top end and the open bottomend; and an axle that is coaxial with and rotatable within the bore, theaxle being laterally secured within the head housing and axially movablewith respect to the head housing, the axle including an engagement endthat extends beyond the open bottom end of the head housing and supportsan FSW tool that is configured to rotate with the axle to effectuatefriction stir welding operations.

In another form, an FSW head is provided comprising: a head housing thatextends from a top end to an open bottom end and defines a boreextending between the top end and the open bottom end; one or morefloating components configured to support an FSW tool, the one or morefloating components being axially movable with respect to the headhousing; and a load cell disposed beneath the open bottom end of thehead housing, the load cell being configured to generate load signals inresponse to axial movement of the floating components.

In yet another form, a method of friction stir welding is provided, themethod comprising: providing a head housing that extends from a top endto an open bottom end and defines a bore extending between the top endand the open bottom end; installing a floating axle in the head housing,the floating axle including an engagement end that extends beyond theopen bottom end, the engagement end supporting an FSW tool; installing aload cell on the open bottom end of the head housing; controllingfriction stir welding with the tool based on load signals generated bythe load cell.

Although the techniques are illustrated and described herein as embodiedin one or more specific examples, the specific details of the examplesare not intended to limit the scope of the techniques presented herein,since various modifications and structural changes may be made withinthe scope and range of the invention. In addition, various features fromone of the examples discussed herein may be incorporated into any otherexamples. Accordingly, the appended claims should be construed broadlyand in a manner consistent with the scope of the disclosure.

We claim:
 1. A friction stir welding head, comprising: a head housingthat extends from a top end to an open bottom end and defines a boreextending between the top end and the open bottom end; an axle that iscoaxial with and rotatable within the bore, wherein the axle: includesan engagement end that extends beyond the open bottom end of the headhousing and supports a friction stir welding tool that is configured torotate with the axle to effectuate friction stir welding operations, thefriction stir welding tool including a shoulder and a pin; and issecured within the head housing so that the axle, the pin, and theshoulder are laterally fixed with respect to the head housing andaxially movable as a single unit with respect to the head housing; and aload cell disposed beneath the open bottom end of the head housing andconfigured to generate load signals in response to axial movement of theaxle, the pin, and the shoulder.
 2. The friction stir welding head ofclaim 1, further comprising: a motor assembly configured to rotate theaxle within the bore and with respect to the head housing.
 3. Thefriction stir welding head of claim 1, wherein the load cell is disposedbetween the open bottom end of the head housing and the friction stirwelding tool supported by the engagement end of the axle.
 4. Thefriction stir welding head of claim 1, wherein the load cell comprises:an inner ring; and an outer ring, the inner ring being fixedly coupledto the axle and movably coupled to the outer ring via a flexibleportion, wherein relative movement of the inner ring with respect to theouter ring causes the load cell to generate the load signals.
 5. Thefriction stir welding head of claim 4, wherein the shoulder and the pinof the friction stir welding tool engage a workpiece to effectuate thefriction stir welding operations and upward forces on the shoulder aretranslated to the inner ring to move the inner ring with respect to theouter ring and cause the load cell to generate the load signals.
 6. Thefriction stir welding head of claim 5, further comprising: a lowerbearing that allows the axle to rotate with respect to the head housing,the lower bearing being coupled to the inner ring via one or morefloating components or formed with the inner ring and the one or morefloating components, wherein the upward forces on the shoulder translateto the inner ring via the lower bearing and the one or more floatingcomponents.
 7. The friction stir welding head of claim 4, wherein thefriction stir welding head further comprises: a stationary shoulder thatcovers the shoulder of the friction stir welding tool, wherein thestationary shoulder and the pin engage a workpiece to effectuate thefriction stir welding operations, and wherein upward forces on thestationary shoulder are translated to the inner ring to move the innerring with respect to the outer ring and cause the load cell to generatethe load signals.
 8. The friction stir welding head of claim 7, whereinthe upward forces translate directly from the stationary shoulder to theinner ring.
 9. A friction stir welding head, comprising: a head housingthat extends from a top end to an open bottom end and defines a boreextending between the top end and the open bottom end; one or morefloating components configured to support a friction stir welding toolincluding a shoulder and a pin, the one or more floating components, theshoulder, and the pin being axially movable as a unit with respect tothe head housing; and a load cell disposed beneath the open bottom endof the head housing, the load cell being configured to generate loadsignals in response to axial movement of the floating components, theshoulder, and the pin.
 10. The friction stir welding head of claim 9,wherein the one or more floating components comprise: an axle that iscoaxial with the bore, the axle including an engagement end thatsupports the friction stir welding tool; one or more bearings that allowrotation of the axle within the bore; and a connector ring that connectsa particular bearing of the one or more bearings to the load cell. 11.The friction stir welding head of claim 10, wherein the one or morefloating components further comprise: an inner ring of the load cell,the inner ring being fixedly coupled to the axle via at least theconnector ring and movably coupled to an outer ring of the load cell viaa flexible portion so that relative movement of the inner ring withrespect to the outer ring causes the load cell to generate the loadsignals.
 12. The friction stir welding head of claim 10, wherein the oneor more floating components further comprise: a rotor of a motorassembly, the rotor being movable by a stator that is fixedly coupled tothe head housing to effectuate rotation of the axle within the bore. 13.The friction stir welding head of claim 10, wherein the particularbearing is a lower bearing disposed between the load cell and a motorassembly included in the friction stir welding head.
 14. The frictionstir welding head of claim 13, wherein the lower bearing furthercomprises: a supplemental bearing housing that is disposed coaxiallyoutward from the lower bearing and is accessible via an access panelincluded on the head housing.
 15. The friction stir welding head ofclaim 9, wherein the friction stir welding head is reconfigurablebetween a rotating shoulder configuration and a stationary shoulderconfiguration with a single installation operation.
 16. A method offriction stir welding, comprising: providing a head housing that extendsfrom a top end to an open bottom end and defines a bore extendingbetween the top end and the open bottom end; installing a floating axlein the head housing, the floating axle including an engagement end thatextends beyond the open bottom end, the engagement end supporting afriction stir welding tool that includes a shoulder and a pin, whereinthe installing secures the floating axle within the head housing so thatthe floating axle, the pin, and the shoulder are laterally fixed withrespect to the head housing and axially movable as a unit with respectto the head housing; installing a load cell on the open bottom end ofthe head housing; and controlling friction stir welding with thefriction stir welding tool based on load signals generated by the loadcell.
 17. The method of friction stir welding of claim 16, wherein thefriction stir welding is rotating shoulder friction stir welding and themethod further comprising: transitioning to stationary shoulder frictionstir welding by installing a stationary shoulder housing onto the loadcell.
 18. The method of friction stir welding of claim 17, wherein thestationary shoulder housing covers the shoulder of the friction stirwelding tool and the transitioning is complete after a single operation.19. The method of claim 16, further comprising: installing one or morefloating components with the floating axle, the floating axle and theone or more floating components being axially movable with the floatingaxle, the pin, and the shoulder.
 20. The method of claim 19, wherein theone or more floating components comprise: one or more bearings thatallow rotation of the floating axle within the bore; a connector ringthat connects a particular bearing of the one or more bearings to theload cell; and at least one of: an inner ring of the load cell, theinner ring being fixedly coupled to the floating axle via at least theconnector ring and movably coupled to an outer ring of the load cell viaa flexible portion so that relative movement of the inner ring withrespect to the outer ring causes the load cell to generate the loadsignals; and a rotor of a motor assembly, the rotor being movable by astator that is fixedly coupled to the head housing to effectuaterotation of the floating axle within the bore.